I know that 4.4BSD-Lite is BSD Licenced. Is it
legal to port BSD Licenced code and change it to
GPL licence?

To quote the BSD License:
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
---> * 1. Redistributions of source code must retain the above copyright
---> * notice, this list of conditions and the following disclaimer.

I.d. you must not change the license. See GPLv2's #2b for the problem
that arises.